Composite reinforcing material and molding material

ABSTRACT

A method of producing the composite reinforcing material includes a step of kneading at least a graphite-based carbon material and a reinforcing material into a base material. The graphite-based carbon material is characterized by having a rhombohedral graphite layer (3R) and a hexagonal graphite layer (2H), wherein a Rate (3R) of the rhombohedral graphite layer (3R) and the hexagonal graphite layer (2H), based on an X-ray diffraction method, which is defined by following Equation 1 is 31% or more:
 
Rate(3 R )= P 3/( P 3+ P 4)×100  (Equation 1)
 
wherein
         P3 is a peak intensity of a (101) plane of the rhombohedral graphite layer (3R) based on the X-ray diffraction method, and   P4 is a peak intensity of a (101) plane of the hexagonal graphite layer (2H) based on the X-ray diffraction method.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending U.S. patent applicationSer. No. 14/764,505, filed Jul. 29, 2015, which is entirely incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a composite reinforcing material and amethod of producing a composite reinforcing material.

BACKGROUND ART

In recent years, addition of various nanomaterials has been studied forpurposes of downsizing and weight saving in various fields. Inparticular, for environmental or resource problems, carbon materialssuch as graphene, CNT (carbon nanotube) and fullerene have attractedattention as nonmetal nanomaterials, and a resin composite reinforcingmaterial in which a reinforcing material (a filler) is dispersed in aresin for a purpose of improving physical properties of the resin(tensile strength, elastic modulus, etc.) has been proposed.

For example, a resin composite reinforcing material in which a carbonmaterial such as flaked graphite is added to a thermoplastic resin suchas polyolefin has been disclosed (Patent Literature 1). Further, acomposite reinforcing material having flaked graphite and an inorganicfiller added thereto for a purpose of improving physical properties(tensile elastic modulus, rigidity, and impact resistance) has beendisclosed (Patent Literature 2 and Patent Literature 3).

Of these, graphene is superior to other carbon materials in aspect ofmass productivity, handleability, etc., as well as performance, andexpectations have been placed on graphene in various fields. However,when a reinforcing material such as graphene is kneaded into a resin,the reinforcing material needs to be dispersed uniformly in order tosufficiently exhibit an improvement effect of physical properties.

In order to obtain high-quality graphene which, for example, has fewergraphite layers, a method in which weak ultrasonic waves are applied tonatural graphite in a solvent (NMP) for a long time (7-10 hours), largeagglomerates which deposit on the bottom are then removed, and thesupernatant is then centrifuged to concentrate it, thereby obtaining agraphene dispersion in which 20% or more of flakes are of a singlelayer, 40% or more of flakes are of double or triple layers, and lessthan 40% of flakes are of 10 layers or more of a graphite material andare dispersed at about 0.5 g/L, has been considered (Patent Literature2).

CITATION LIST Patent Literature

PTL 1: JP-A-2010-254822 ([0032]-[0038])

PTL 2: JP-A-2014-201676 ([0048]-[0064])

PTL 3: JP-A-2014-210916 ([0043])

PTL 4: WO 2014/064432 (lines 4-9 on page 19)

PTL 5: JP-A-2013-079348 ([0083])

PTL 6: JP-A-2009-114435 ([0044])

Non Patent Literature

NPL 1: Structural Change of Graphite with Griding; authors: MichioINAGAKI, Hisae MUGISHIMA, and Kenji HOSOKAWA; Feb. 1, 1973 (Received)

NPL 2: Changes of Probabilities P1, PABA, PABC with Heat Treatment ofCarbons; authors: Tokiti NODA, Masaaki IWATSUKI, and Michio INAGAKI;Sep. 16, 1966 (Received)

NPL 3: Spectroscopic and X-ray diffraction studies on fluid depositedrhombohedral graphite from the Eastern Ghats Mobile Belt, India; G.Parthasarathy, Current Science, Vol. 90, No. 7, 10 Apr. 2006

NPL 4: Classification of solid carbon materials and their structuralcharacteristics; Nagoya Institute of Technology; Shinji KAWASAKI

SUMMARY OF INVENTION Technical Problem

However, the methods disclosed in Patent Literatures 1, 2 and 3 usecommercially available flaked graphite, which is hardly dispersed simplyby kneading due to aggregating nature of the flaked graphite, thus aneffect of flaked graphite is not sufficiently obtained. However, evenwhen the graphite material (20% or more of flakes of a single layer, 40%or more of flakes of double or triple layers, and less than 40% offlakes of 10 layers or more) obtained by the method disclosed in PatentLiterature 4 was mixed into a solvent, the amount of graphene dispersedin the solvent was small, and only a dilute graphene dispersion could beobtained. Additionally, although it is considered that a supernatant iscollected and concentrated, it takes a long time for treatments torepeat the steps of collecting and concentrating the supernatant, andthere is a problem of inferior production efficiency of a graphenedispersion. As disclosed in Patent Literature 4, even by subjectingnatural graphite to an ultrasonic treatment for a long time, only weakparts of the surface are exfoliated, other large parts do not contributeto the exfoliation, and it is considered as a problem that the amount ofexfoliated graphene is small.

Further, in order to increase mechanical strength, a reinforcingmaterial is generally added to a base material such as a polymer,however, depending on an addition amount of a reinforcing material,original properties (outer appearance) of a polymer may be affected(Patent Literature 5).

In Patent Literatures 2 and 3 mentioned above, physical propertiescontributing to rigidity (hardness), such as a elastic modulus andimpact resistance are improved by adding a reinforcing material. Similarresults were obtained in Example 5 of the present specification(undisclosed invention before making the present application).

Further, for a purpose of improving strength of tensile (tensilestrength), addition of a reinforcing material has been performed (e.g.,Patent Literature 1). In general, in order to increase the tensilestrength, a reinforcing material (a filler) is suitably a string-likematerial that includes carbon fibers, glass fibers, cellulose fibers,and the like. It has been further proposed that tensile yield stress isincreased by using a compatibilizer for a purpose of preventing astring-like material from coming off a base material (Patent Literature6). However it has been found that mechanical strength and the like thatinclude tensile strength, etc. are not sufficiently improved just byadding a string-like material. The reason is considered that a basematerial is too soft so that a string-like material comes off togetherwith the base material.

As mentioned above, there has been a problem that an amount of graphenethat is exfoliated is normally small by processing natural graphitewithout any treatments. However, as a result of earnest studies, bycarrying out predetermined treatments to graphite serving as a sourcematerial, there is obtained a graphite-based carbon material (a grapheneprecursor), from which graphene is easily exfoliated, the graphene beingable to be dispersed at a high concentration or to a high degree. A partor whole of the graphene precursor is exfoliated by ultrasonic waves,stirring and kneading to produce a mixed material being “graphene-likegraphite”, containing material from the graphene precursor to graphene.A size, thickness, etc. of the graphene-like graphite is not limitedsince they are variable depending on an addition amount, a process time,etc. of the graphene precursor, however, it is preferred that thegraphene-like graphite is more flaked. That is, in another words, thegraphite-based carbon material (the graphene precursor) is graphitecapable of being easily exfoliated and dispersed as the graphene-likegraphite by existing stirring and kneading processes or devices.

It was found that, by dispersing a small amount of the graphene-likegraphite together with a reinforcing material in a base material,mechanical strength, such as bending modulus, compressive strength,tensile strength, and Young's modulus, could be improved. Moreover, itwas found that the composite reinforcing material could be producedwithout substantially changing a conventional production method.

The invention has been completed focusing on such problems and an objectof the invention is to provide a composite reinforcing material and amethod of producing a composite reinforcing material excellent inmechanical strength.

Another object of the invention is to provide a composite reinforcingmaterial capable of exhibiting desired characteristics even though anamount of graphene-like graphite dispersed/added in a base material issmall.

Yet another object of the invention is to provide a compositereinforcing material excellent in mechanical strength by using aconventional production process.

Solution to Problem

In order to solve the above-described problems, a method of producing acomposite reinforcing material of the present invention comprises a stepof kneading at least a graphite-based carbon material and a reinforcingmaterial into a base material,

the graphite-based carbon material having a rhombohedral graphite layer(3R) and a hexagonal graphite layer (2H), wherein a Rate (3R) of therhombohedral graphite layer (3R) and the hexagonal graphite layer (2H),based on an X-ray diffraction method, which is defined by followingEquation 1 is 31% or more:Rate(3R)=P3/(P3+P4)×100  Equation 1wherein

P3 is a peak intensity of a (101) plane of the rhombohedral graphitelayer (3R) based on the X-ray diffraction method, and

P4 is a peak intensity of a (101) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method.

Furthermore, a composite reinforcing material being produced by kneadingat least a graphite-based carbon material and a reinforcing materialinto a base material, thereby exfoliating a part or whole of thegraphite-based carbon material,

the graphite-based carbon material having a rhombohedral graphite layer(3R) and a hexagonal graphite layer (2H), wherein a Rate of therhombohedral graphite layer (3R) and the hexagonal graphite layer (2H),based on an X-ray diffraction method, which is defined by followingEquation 1 is 31% or more:Rate(3R)=P3/(P3+P4)×100  Equation 1wherein

P3 is a peak intensity of a (101) plane of the rhombohedral graphitelayer (3R) based on the X-ray diffraction method, and

P4 is a peak intensity of a (101) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method.

Furthermore, a composite reinforcing material comprises at least areinforcing material, graphene-like graphite exfoliated from agraphite-based carbon material, and a reinforcing material, dispersed ina base material,

the graphite-based carbon material characterized by having arhombohedral graphite layer (3R) and a hexagonal graphite layer (2H),wherein a Rate (3R) of the rhombohedral graphite layer (3R) and thehexagonal graphite layer (2H), based on an X-ray diffraction method,which is defined by following Equation 1 is 31% or more:Rate(3R)=P3/(P3+P4)×100  (Equation 1)wherein

P3 is a peak intensity of a (101) plane of the rhombohedral graphitelayer (3R) based on the X-ray diffraction method, and

P4 is a peak intensity of a (101) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method.

According to the features, the composite material is excellent inmechanical strength. This is because, it is speculated that, the effectof increasing an elastic modulus of a base material itself and theeffect of preventing a reinforcing material from coming off weresynergistically exhibited by dispersing graphene-like graphite in a basematerial. Among mechanical strength such as bending modulus, compressivestrength, tensile strength, and Young's modulus, the composite materialis excellent in the tensile strength as one example.

The reinforcing material is characterized by being a microparticle in astring-like, linear, or flake-like shape.

According to the feature, the microparticle is surrounded by thegraphene-like graphite, thus a reinforcing function of the microparticlecan be sufficiently exerted.

The microparticle is characterized by having an aspect ratio of 5 ormore.

According to the feature, a reinforcing function of the microparticlecan be further sufficiently exerted.

A weight ratio of the sum of the graphite-based carbon material andgraphene-like graphite to the reinforcing material is characterized bybeing 1/100 or more and less than 10.

According to the feature, a reinforcing function of the reinforcingmaterial can be efficiently exerted.

The base material is characterized by being a polymer.

According to the feature, a composite reinforcing material excellent inmechanical strength can be obtained.

The base material is characterized by being an inorganic material.

According to the feature, a composite reinforcing material excellent inmechanical strength can be obtained.

A molding material is characterized by comprising the compositereinforcing material.

According to the feature, a molding material used for 3D printing andthe like, excellent in mechanical strength, can be obtained.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a) and 1(b) are figures which show a crystal structure ofgraphite, where 1(a) refers to a crystal structure of hexagonalcrystals, and 1(b) refers to a crystal structure of rhombohedralcrystals.

FIG. 2 is a diagram which shows an X-ray diffraction profile of generalnatural graphite.

FIG. 3 is a diagram which illustrates a production apparatus A using ajet mill and plasma of Example 1.

FIG. 4 is a figure which illustrates a production apparatus Busing aball mill and magnetron of Example 1, where 4(a) is a diagram whichillustrates a pulverizing state, and 4(b) is a diagram which illustratesa state where graphite-based carbon materials (precursors) arecollected.

FIG. 5 is a diagram which shows an X-ray diffraction profile of agraphite-based carbon material of Sample 5 produced by the productionapparatus B according to Example 1.

FIG. 6 is a diagram which shows an X-ray diffraction profile of agraphite-based carbon material of Sample 6 produced by the productionapparatus A according to Example 1.

FIG. 7 is a diagram which shows an X-ray diffraction profile of agraphite-based carbon material of Sample 1 indicating a comparativeexample.

FIG. 8 is a diagram which shows a dispersion-producing apparatus whichproduces a dispersion using a graphite-based carbon material as aprecursor.

FIG. 9 is a diagram which shows dispersing states of dispersionsproduced by using graphite-based carbon materials of Sample 1 indicatinga comparative example, and Sample 5 produced by the production apparatusB of Example 1.

FIGS. 10(a) and (b) are TEM images of a graphite-based carbon material(graphene) dispersed in a dispersion.

FIGS. 11(a) and 11(b) are figures which shows distribution states of agraphite-based carbon material dispersed in a dispersion which wasproduced using a graphite-based carbon material (precursor) of Sample 5,where 11(a) is a diagram which shows an average size distribution, while11(b) is a diagram which shows a distribution of the number of layers.

FIGS. 12(a) and 12(b) are figures which show a distribution state of agraphite-based carbon material dispersed in a dispersion which wasproduced using a graphite-based carbon material of Sample 1 indicatingthe comparative example, where 12(a) is a diagram showing an averagesize distribution, and 12(b) is a diagram showing a distribution of thenumber of layers.

FIG. 13 is a diagram which shows distributions of the number of layersof graphite-based carbon materials each dispersed in dispersions thatwere produced using Samples 1 to 7 as precursors.

FIG. 14 is a diagram which shows proportions of graphene having 10layers or less to a content of rhombohedral crystals dispersed in adispersion.

FIGS. 15(a) and 15(b) are figures which show a distribution state ofgraphite when varying conditions for producing a dispersion using agraphite-based carbon material (precursor) of Sample 5 according toExample 2, where 15(a) is a diagram showing a distribution in a casewhere an ultrasonic treatment and a microwave treatment were combined,while 15(b) is a diagram showing a distribution of the number of layersin a case where an ultrasonic treatment was conducted.

FIG. 16 is a diagram which shows a resistance value when agraphite-based carbon material of Example 3 was dispersed in aconductive ink.

FIG. 17 is a diagram which shows a tensile strength when agraphite-based carbon material of Example 4 was kneaded with a resin.

FIG. 18 is a diagram which shows an elastic modulus when agraphite-based carbon material of Example 5 was kneaded with a resin.

FIGS. 19(a) and 19(b) are figures which show distribution states of agraphite-based carbon material in a dispersion, dispersed inN-methylpyrrolidone (NMP), for providing a supplementary description ofa dispersing state of Example 5, where 19(a) is a distribution state ofsample 12 and 19(b) is a distribution state of sample 2.

FIG. 20 is a graph which shows a tensile strength and a bending modulusof a test piece of Example 6.

FIG. 21 is a SEM photographed image (plan view) of a graphene precursor.

FIG. 22 is a SEM photographed image (side view) of a graphene precursor.

FIG. 23 is a SEM photographed image (cross-section view) of a resin inwhich graphene-like graphite was dispersed.

FIG. 24 is a SEM photographed side image (side view) of thegraphene-like graphite in FIG. 23.

FIG. 25 is a graph which shows a tensile strength and a bending modulusof a test piece of Example 7.

FIG. 26 is a graph which shows a tensile strength and a bending modulusof a test piece of Example 8 in which a shape of a reinforcing materialwas changed.

FIGS. 27(a) and 27(b) are schematic views which illustrate a shape of areinforcing material of Example 8, where 27(a) is a shape of glassfibers and carbon fibers, 27(b) is a shape of talc, and 27(c) is a shapeof silica.

FIG. 28 is a graph which shows a tensile strength and a bending modulusof a test piece of Example 9 in which a mixture ratio of a grapheneprecursor to a reinforcing material was changed.

DESCRIPTION OF EMBODIMENTS

The invention focuses on a crystal structure of graphite, and, at first,matters relating to the crystal structure will be explained. It has beenknown that natural graphite is classified into three types of crystalstructures, namely hexagonal crystals, rhombohedral crystals anddisordered crystals, depending on an overlapping manner of layers. Asshown in FIG. 1, hexagonal crystals have a crystal structure in whichlayers are arranged in the order of ABABAB . . . , while rhombohedralcrystals have a crystal structure in which layers are arranged in theorder of ABCABCABC . . . .

In natural graphite, there are almost no rhombohedral crystals in astage where natural graphite is excavated. However, about 14% ofrhombohedral crystals exist in general natural graphite-based carbonmaterials because pulverization or the like is carried out in apurification stage. In addition, it has been known that a proportion ofrhombohedral crystals converges on about 30% even when pulverization iscarried out during purification for a long time (Non-Patent Literatures1 and 2)

Moreover, a method in which graphite is expanded by heating, rather thanwith physical forces such as pulverization, thereby flaking thegraphite. However, even when graphite is treated with a heat of 1600 K(about 1,300° C.), a proportion of rhombohedral crystals is about 25%(Non-Patent Literature 3) Furthermore, the proportion is up to about 30%even when heat of an extremely high temperature of 3000° C. is appliedthereto (Non-Patent Literature 2)

Thus, although it is possible to increase a proportion of rhombohedralcrystals by treating natural graphite with physical forces or heat, theupper limit is about 30%.

Hexagonal crystals (2H), which are included in natural graphite at ahigh level, are very stable, and an interlayer van der Waals forcebetween their graphene layers is shown by Equation 3 (Patent Literature2). By applying an energy exceeding this force, graphene is exfoliated.An energy required for the exfoliation is inversely proportional to thecube of the thickness. Therefore, in a thick state where numerous layersare overlapped, graphene is exfoliated by a weak physical force such asby very feeble ultrasonic waves. However, in a case where graphene isexfoliated from somewhat thin graphite, a very large energy is required.In other words, even if graphite is treated for a long time, only weakparts of the surface are exfoliated, and large parts remain notexfoliated.Fvdw=H·A/(6π·t ³)  Equation 3

Fvdw: Van der Waals' force

H: Hamaker constant

A: Surface area of graphite or graphene

t: Thickness of graphite or graphene

The present inventors succeeded in increasing a proportion ofrhombohedral crystals (3R), which had been increased to only about 30%by treatments of pulverization or heating to an extremely hightemperature, to 30% or more by carrying out predetermined treatments, asshown below, to natural graphite. The following findings were obtainedas results of experiments and studies. That is, when a content ofrhombohedral crystals (3R) in a graphite-based carbon material ishigher, particularly when the content is 31% or more, there is atendency that graphene is easily exfoliated by use of such agraphite-based carbon material as a precursor, thereby easily obtaininga highly concentrated and dispersed graphene dispersion or the like. Forthe reason, it is considered that, when a shear force or the like isapplied to rhombohedral crystals (3R), a deformation occurs betweenlayers, i.e. a deformation in the entire structure of the graphitebecomes large, and graphene is easily exfoliated independently of thevan der Waals' force. Accordingly, in the invention, a graphite-basedcarbon material, from which graphene is easily exfoliated by carryingout predetermined treatments to natural graphite, and which makes itpossible to disperse graphene at a high concentration or to a highdegree, is called a graphene precursor. Hereinafter, a method ofproducing a graphene precursor showing predetermined treatments, acrystal structure of the graphene precursor, and a graphene dispersionusing the graphene precursor will be described in that order in examplesbelow.

Here, in the specification, a graphene refers to a flake-like orsheet-like graphene which is a crystal of a mean size of 100 nm or morebut which is not a fine crystal of a mean size of several nanometers totens of nanometers, and which has 10 layers or less.

Additionally, since graphene is a crystal with a mean size of 100 nm ormore, when artificial graphite and carbon black, which are amorphous(microcrystal) carbon materials other than natural graphite, are eventreated, graphene cannot be obtained (Non-Patent Literature 4)

Further, in the specification, a graphene composite means a compositewhich is produced by using the graphite-based carbon material useful asa graphene precursor according to the invention, i.e. a graphite-basedcarbon material having a Rate (3R) of 31% or more (e.g. Samples 2-7 ofExample 1, samples 2, 21, . . . of Example 5 described below)

Hereinafter, examples for carrying out the composite reinforcingmaterial and the molding material according to the present inventionwill be described.

EXAMPLE 1

<As to Production of a Graphite-based Carbon Material Useful as aGraphene Precursor>

A method for obtaining a graphite-based carbon material useful as agraphene precursor by a production apparatus A using a jet mill andplasma shown in FIG. 3 will be explained. As an example, the productionapparatus A refers to a case in which plasma is applied for theradiowave-force-based treatment and in which the jet mill is used forthe physical-force-based treatment.

In FIG. 3, the symbol 1 refers to a particle of 5 mm or less of anatural graphite material (flaky graphite ACE-50 manufactured by NipponGraphite Industries, ltd.); the symbol 2 refers to a hopper which storesthe natural graphite material 1; the symbol 3 refers to a Venturi nozzlewhich discharges the natural graphite material 1 from the hopper 2; thesymbol 4 refers to a jet mill which jets the air which has been pumpedfrom a compressor 5, while being divided into eight places, to therebyallow the natural graphite material to collide against the inside of achamber by a jet blast; and the symbol 7 refers to a plasma generatorwhich sprays a gas 9, such as oxygen, argon, nitrogen or hydrogen,through a nozzle 8 from a tank 6 and which applies a voltage to a coil11, wound around the outer periphery of the nozzle 8, from ahigh-voltage power supply 10, thereby generating plasma inside thechamber of the jet mill 4, and the plasma generator is provided in eachof four places inside the chamber. The symbol 13 refers to a pipe whichconnects the jet mill 4 and a dust collector 14 to one another; thesymbol 14 refers to a dust collector; the symbol 15 refers to acollection container; the symbol 16 refers to a graphite-based carbonmaterial (graphene precursor); and the symbol 17 refers to a blower.

Next, the production method will be explained. Conditions for the jetmill and plasma are as follows.

The conditions for the jet mill are as follows.

Pressure: 0.5 MPa

Air volume: 2.8 m³/min

Nozzle inner Diameter: 12 mm

Flow rate: about 410 m/s

The conditions for plasma are as follows.

Output: 15 W

Voltage: 8 kV

Gas species: Ar (purity 99.999 vol %)

Gas flow rate: 5 L/min

It is considered that the natural graphite materials 1, which have beencharged into the chamber of the jet mill 4 from the Venturi nozzle 3,are accelerated to the sonic velocity or higher inside the chamber, andare pulverized by impact between the natural graphite materials 1 or byimpact of them against the wall, and that, simultaneously, the plasma 12discharges an electric current or excites the natural graphite materials1, acts directly on atoms (electrons), and increases deformations ofcrystals, thereby promoting the pulverization. When the natural graphitematerials 1 turn into fine particles of a certain particle diameter(about 1 to 10 μm), their mass is reduced, the centrifugal force isweakened, and, consequently, the natural graphite materials 1 are pumpedout from the pipe 13 which is connected to the center of the chamber.

A gas including graphite-based carbon materials (graphene precursors),which have been flowed from the pipe 13 into a cylindrical container ofthe chamber of the dust collector 14, forms a spiral flow, and drops thegraphite-based carbon materials 16, which collide with the internal wallof the container, to a collection container 15 below, while an ascendingair current generates in the center of the chamber due to a taperedcontainer part of the downside of the chamber, and the gas is emittedfrom the blower 17 (so-called cyclone effects). According to theproduction apparatus A in this example, about 800 g of a grapheneprecursor from 1 kg of the raw materials, i.e. natural graphitematerials 1, is used. The graphite-based carbon material (grapheneprecursors) 16 was obtained (recovery efficiency: about 80%)

Next, based on the production apparatus B using a ball mill andmicrowaves shown in FIG. 4, a method for obtaining a graphite-basedcarbon material useful as a graphene precursor will be described. Theapparatus B refers to, as an example, a case where microwaves areapplied as the radiowave-force-based treatment and where a ball mill isused for the physical-force-based treatment.

In FIGS. 4(a) and (b), the symbol 20 refers to the ball mill; the symbol21 refers to a microwave generator (magnetron); the symbol 22 refers toa wave guide; the symbol 23 refers to a microwave inlet; the symbol 24refers to a media; the symbol 25 refers to particles of 5 mm or less ofa natural graphite material (flaky graphite ACB-50 manufactured byNippon Graphite Industries, ltd.); the symbol 26 refers to a collectioncontainer; the symbol 27 refers to a filter; and the symbol 28 refers tographite-based carbon material (graphene precursors)

Next, the production method will be explained. Conditions for the ballmill and the microwave generator are as follows.

The conditions for the ball mill are as follows.

Rotational speed: 30 rpm

Media size: φ5 mm

Media species: zirconia balls

Pulverization time: 3 hours

The conditions for the microwave generator (magnetron) are as follows.

Output: 300 N

Frequency; 2.45 GHz

Irradiation method: Intermittent

1 kg of natural graphite carbon raw materials 25 and 800 g of media 24are charged into the chamber of the ball mill 20, the chamber is closed,and the mixture is treated at a rotational speed of 30 rpm for 3 hours.During the treatment, microwaves are irradiated intermittently (for 20seconds every 10 minutes) to the chamber. It is considered that themicrowave irradiation acts directly on atoms (electrons) of the rawmaterials, thus increasing deformations of the crystals. After thetreatment, media 24 are removed by the filter 27, and thus, powder ofabout 10 μm of graphite-based carbon materials (precursors) 28 can becollected in the collection container 26.

<As to an X-Ray Diffraction Profile of Graphite-based Carbon Materials(Graphene Precursors)>

With reference to FIGS. 5 to 7, X-ray diffraction profiles and crystalstructures will be described with respect to graphite-based naturalmaterials (Samples 6 and 5) produced by the production apparatuses A andB, and the powder of about 10 μm of graphite-based natural materials(Sample 1: a comparative example) obtained by using only the ball millof the production apparatus B.

The measurement conditions for the X-ray diffraction apparatus are asfollows.

Source: Cu Kα ray

Scanning speed: 20°/min

Tube voltage: 40 kV

Tube current: 30 mA

According to the X-ray diffraction method(horizontal-sample-mounting-model multi-purpose X-ray diffractometerUltima IV manufactured by Rigaku Corporation), each sample shows peakintensities P1, P2, P3 and P4 in the planes (100), (002) and (101) ofhexagonal crystals 2H and in the plane (101) of rhombohedral crystals3R. Therefore, these peak intensities will be explained.

Here, the measurements of X-ray diffraction profile have been used theso-called standardized values at home and abroad in recent years. Thishorizontal-sample-mounting-model multi-purpose X-ray diffractometerUltima IV manufactured by Rigaku Corporation is an apparatus which canmeasure X-ray diffraction profile in accordance with JIS R 7651:2007“Measurement of lattice parameters and crystallite sizes of carbonmaterials”. In addition, Rate (3R) is the ratio of the diffractionintensity obtained by the Rate (3R)=P3/(P3+P4)×100, even if the value ofthe diffraction intensity is changed, the value of Rate (3R) is notchanges. Means that the ratio of the diffraction intensity isstandardized, it is commonly used to avoid performing the identificationof the absolute value substance and its value does not depend onmeasurement devices.

As shown in FIG. 5 and Table 1, Sample 5 produced by the productionapparatus B, which applies a treatment with a ball mill and a microwavetreatment, had high rates of peak intensities P3 and P1, and a Rate (3R)defined by Equation 1 showing a rate of P3 to a sum of P3 and P4 was46%. Additionally, the intensity ratio P1/P2 was 0.012.Rate(3R)=P3/(P3+P4)×100  Equation 1wherein

P1 is a peak intensity of a (100) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method,

P2 is a peak intensity of a (002) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method,

P3 is a peak intensity of a (101) plane of the rhombohedral graphitelayer (3R) based on the X-ray diffraction method, and

P4 is a peak intensity of a (101) plane of the hexagonal graphite layer(2H) based on the X-ray diffraction method.

TABLE 1 Peak intensities [counts · deg] (2θ [°]) Hexagonal crystals 2H(100) 162 [P1] (42.33) Hexagonal crystals 2H (002) 13157 [P2] (26.50)Rhombohedral crystals 3R (101) 396 [P3] (43.34) Hexagonal crystals 2H(101) 466 [P4] (44.57)

In the same manner, as shown in FIG. 6 and Table 2, Sample 6 produced bythe production apparatus A, which applies a treatment based on the jetmill and a treatment based on plasma, had high rates of peak intensitiesP3 and P1, and the Rate (3R) was 51%. In addition, the intensity ratioP1/P2 was 0.014.

TABLE 2 Peak intensities [counts · deg] (2θ [°]) Hexagonal crystals 2H(100) 66 [P1] (42.43) Hexagonal crystals 2H (002) 4,675 [P2] (26.49)Rhombohedral crystals 3R (101) 170 [P3] (43.37) Hexagonal crystals 2H(101) 162 [P4] (44.63)

Furthermore, as shown in FIG. 7 and Table 3, Sample 1 indicating acomparative example produced with only the ball mill had a small rate ofa peak intensity P3, compared with Samples 5 and 6, and the Rate (3R)was 23%. In addition, the intensity ratio P1/P2 was 0.008.

TABLE 3 Peak intensities [counts · deg] (2θ [°]) Hexagonal crystals 2H(100) 120 [P1] (42.4) Hexagonal crystals 2H (002) 15,000 [P2] (26.5)Rhombohedral crystals 3R (101) 50 [P3] (43.3) Hexagonal crystals 2H(101) 160 [P4] (44.5)

Thus, Sample 5 produced by the production apparatus B of Example 1, andSample 6 produced by the production apparatus A of Example 1 had Rates(3R) of 46% and 51%, respectively, and it was shown that their Rates(3R) were 40% or more, or 50% or more, compared with the naturalgraphite shown in FIG. 2 and Sample 1 indicating a comparative example.

Next, graphene dispersions were produced using the above-producedgraphene precursors, and their easiness in exfoliation of graphene wasevaluated.

<As to Graphene Dispersions>

A method for producing a graphene dispersion will be explained withreference to FIG. 8. FIG. 8 shows, as an example, a case where anultrasonic treatment and a microwave treatment are combined in a liquidwhen a graphene dispersion is produced.

-   (1) 0.2 g of a graphite-based carbon material useful as a graphene    precursor and 200 ml of N-methylpyrrolidone (NMP) which serves as    dispersing medium are charged to a beaker 40.-   (2) The beaker 40 is put into a chamber 42 of a microwave generator    43, and an ultrasonic trembler 44A of an ultrasonic horn 44 is    inserted into dispersing medium 41 from the upper direction.-   (3) The ultrasonic horn 44 is activated, and ultrasonic waves of 20    kHz (100 W) are continuously applied thereto for 3 hours.-   (4) While the above ultrasonic horn 44 is actuated, the microwave    generator 43 is activated to apply microwaves of 2.45 GHz (300 W)    intermittently (irradiation for 10 seconds every 5 minutes) thereto.

FIG. 9 refers to appearances of graphene dispersions produced in theabove-described way when 24 hours had passed.

Although a portion of the graphene dispersion 30 using Sample 5 producedby the production apparatus B was deposited, a product entirely showinga black color was observed. For this, it is considered that a largeportion of the graphite-based carbon materials used as grapheneprecursors are dispersed in a state where graphene is exfoliated fromthem.

In the dispersion 31 using Sample 1 indicating a comparative example,most of the graphite-based carbon materials were deposited, and it wasconfirmed that a portion thereof floated as a supernatant. From thefacts, it is considered that graphene was exfoliated from a smallportion thereof and that they floated as the supernatant.

Furthermore, the graphene dispersion produced in the above-described waywas diluted to an observable concentration, was coated onto a samplestage (TEM grid), and the grid was dried. Thus, the size and the numberof layers of graphene was observed in the captured image of atransmission electron microscope (TEM), as shown in FIG. 10. Inaddition, the grid coated with the diluted supernatant was used forSample 1. For example, in the case of FIG. 10, the size corresponds to amaximum length L of a flake 33, which was 600 nm, based on FIG. 10(a).As for the number of layers, the end face of the flake 33 was observedin FIG. 10(b), and overlapping graphene layers were counted, therebycalculating the number of layers as 6 layers (a portion indicated by thesymbol 34). In this way, the size and the number of layers were measuredwith respect to each flake (“N” indicates the number of flakes), and thenumbers of graphene layers and the sizes shown in FIGS. 11 and 12 wereobtained.

With reference to FIG. 11(a), a particle size distribution (distributionof sizes) of thin flakes included in the graphene dispersion of Sample 5(Rate (R3) of 46%) produced by the production apparatus B of Example 1was a distribution having a peak of 0.5 μm. In addition, in FIG. 11(b),as to the number of layers, a distribution which had a peak in 3 layersand in which graphene having 10 layers or less were 68% was observed.

With reference to FIG. 12, a particle size distribution (distribution ofsizes) of thin flakes included in the dispersion of Sample 1 (Rate (R3)of 23%) of the comparative example was a distribution having a peak of0.9 μm. In addition, as for the number of layers, a distribution inwhich those having 30 layers or more occupied the greater portion and inwhich graphene having 10 layers or less were 10% was observed.

From the results, it was revealed that, when the product of Sample 5produced by the production apparatus B was used as a graphene precursor,a highly-concentrated graphene dispersion which contains plenty ofgraphene of 10 layers or less and which has excellent dispersibility ofgraphene can be obtained.

Next, with reference to FIG. 13, a relation between the Rate (3R) of thegraphene precursor and the number of layers in the graphene dispersionwill be described. Samples 1, 5 and 6 in FIG. 13 are those describedabove. Samples 2, 3 and 4 were produced by the production apparatus Bwhich carried out a treatment based on a ball mill and a microwavetreatment, and were graphene dispersions produced using grapheneprecursors which had been produced by making the irradiating time ofmicrowaves shorter than that for Sample 5. In addition, Sample 7 wasproduced by the production apparatus A which carried out a treatmentbased on a jet mill and a plasma treatment, and was a graphenedispersion produced by using a graphene precursor which had beenproduced by applying plasma of a higher output than that for Sample 6.

From FIG. 13, as to Samples 2 and 3 showing Rates (3R) of 31% and 38%,respectively, the distributions of the number of layers have peaks ataround 13 as the number of layers; that is, the shapes of thedistributions are close to that of a normal distribution (dispersionsusing Samples 2 and 3). As to Samples 4 to 7 showing Rates (3R) of 40%or more, the distributions of the number of layers have peaks at severalas the number of layers (thin graphene); that is, the shapes of thedistributions are those of a so-called lognormal distribution. On theother hand, as to Sample 1 having a Rate (3R) of 23%, the distributionthereof has a peak at 30 or more as the number of layers (a dispersionusing Sample 1). That is, it is understood as follows: there is atendency that, in cases where the Rate (3R) reaches 31% or more, theshapes of the layer number distributions differ from those for caseswhere the Rate (3R) is less than 31%; and further, in cases where theRate (3R) reaches 40% or more, the shapes of the layer numberdistributions clearly differ from those for cases where the Rate (3R) isless than 40%. In addition, it can be understood that, as to proportionsof graphene of 10 layers or less, the Rate (3R) of the dispersion usingSample 3 is 38%, while the Rate (3R) of the dispersion using Sample 4 is62%, and that, when the Rate (3R) reaches 40% or more, a proportion ofgraphene of 10 layers or less rapidly increases.

From these facts, it can be considered that graphene of 10 layers orless are easily exfoliated in cases where the Rate (3R) is 31% or more,and that, as the Rate (3R) increases to 40%, 50% and 60%, graphene of 10layers or less are more easily exfoliated. In addition, focusing on theintensity ratio P1/P2, Samples 2 to 7 show values within a comparativelynarrow range of 0.012 to 0.016, and any of them are preferable becausethey exceed 0.01 where it is considered that graphene is easilyexfoliated since crystal structures will be deformed.

Furthermore, results obtained by comparing Rates (3R) and proportions ofgraphene of 10 layers or less included therein are shown in FIG. 14.With reference to FIG. 14, it was revealed that, when the Rate (3R)reached 25% or more, around 31%, graphene of 10 layers or less startedto increase (showing an ever-increasing slope) Further, it was revealedthat, around 40%, graphene of 10 layers or less rapidly increased (as toproportions of graphene of 10 layers or less, whereas the Rate (3R) ofthe dispersion using Sample 3 was 38%, the Rate (3R) of the dispersionusing Sample 4 was 62%, and the proportion of graphene of 10 layers orless rapidly increased by 24% as the Rate (3R) increased by 4%), andthat a percentage of graphene of 10 layers or less against the totalgraphene was 50% or more. In addition, the points of black squares inFIG. 14 each correspond to different samples, and above-describedSamples 1 to 7 and other samples are included therein.

From the facts, when a sample showing a Rate (3R) of 31% or more is usedas a graphene precursor to produce a graphene dispersion, the proportionof distributed graphene of 10 layers or less starts increasing; further,when a sample showing a Rate (3R) of 40% or more is used as a grapheneprecursor to produce a graphene dispersion, 50% or more of graphene of10 layers or less are produced. In other words, a graphene dispersion inwhich graphene is highly concentrated and highly dispersed can beobtained. Furthermore, because almost no graphite-based carbon materials(precursors) included in the dispersion deposit as described above, aconcentrated graphene dispersion can easily be obtained. According tothis method, even a graphene dispersion whose graphene concentrationexceeded 10% can be produced without concentrating it. Particularly, theRate (3R) is preferably 40% or more from a view point that theproportion of dispersed graphene of 10 layers or less sharply increasesto 50% or more.

The above description clarifies the following: when the Rate (3R) is 31%or more, preferably 40% or more, and further preferably 50% or more,separation into graphene of 10 layers or less and thin graphite-basedcarbon materials of around 10 layers occurs in a greater proportion inmany cases; and in the case where these graphite-based carbon materialsare used as graphene precursors, a highly-concentrated graphenedispersion that has excellent dispersibility of graphene can beobtained. Still further, Example 5 to be described below clarifies that,in the case where the Rate (3R) is 31% or more, graphite-based carbonmaterials are useful as a graphene precursor.

Furthermore, an upper limit for the Rate (3R) is considered that theupper limit is not particularly defined. However, it is preferable thatthe upper limit is defined such that the intensity ratio P1/P2simultaneously satisfies 0.01 or more, because graphene precursors areeasily exfoliated when a dispersion or the like is produced. Inaddition, in cases of production methods using production apparatuses Aand B, the upper limit is about 70%, from a viewpoint that graphene iseasily produced. Also, a method combining a treatment based on the jetmill of the production apparatus A and a plasma treatment is morepreferable, because a graphene precursor having a higher Rate (3R) caneasily be obtained. Additionally, the Rate (3R) as long as it reaches31% or more by combining the physical-force-based treatment and theradiowave-force-based treatment.

EXAMPLE 2

In Example 1, a case where the ultrasonic treatment and the microwavetreatment were combined for obtaining a graphene dispersion isexplained. In Example 2, only an ultrasonic treatment was carried outwhile a microwave treatment was not carried out, and other conditionswere the same as those for Example 1,

FIG. 15(b) shows a distribution of a number of layers with respect to agraphene dispersion which was obtained by carrying out an ultrasonictreatment using the graphene precursor of Sample 5 (Rate (3R)=46%)produced by the production apparatus B. In addition, FIG. 15(a) is thesame as the distribution shown in FIG. 11(b) of Sample 5 produced by theproduction apparatus B of Example 1.

As a result, although the tendency of the distribution of the number oflayers was almost similar, a proportion of graphene of 10 layers or lesswas 64%, and was slightly decreased, compared with 68% of Example 1.From the fact, it was revealed that it was more effective tosimultaneously carry out two of the treatments based on a physical forceand a radiowave force for producing a graphene dispersion.

EXAMPLE 3

In Example 3, an example used for a conductive ink will be described.

Sample 1 (Rate (3R)=23%), Sample 3 (Rate (3R)=38%), Sample 5 (Rate(3R)=46%) and Sample 6 (Rate (3R)=51%) of Example 1 were used asgraphene precursors in mixture solution of water and an alcohol of thecarbon number of 3 or less, which severed as a conductivity-impartingagent, at concentrations adopted for conductive inks, thus producingINK1, INK3, INK5 and INK6, and their resistance values were compared.Based on the results, as the Rates (3R) became higher, the resistancevalues were lower.

EXAMPLE 4

In Example 4, an example in which a graphene precursor was kneaded witha resin will be explained.

When a resin sheet, in which graphene was dispersed, was produced, thetensile strength was very superior although glass fibers were addedthereto. Therefore, a factor for this was studied, and, consequently, afinding that a compatibilizer added simultaneously with the glass fiberscontributed to formation of graphene from the precursor could beobtained. Therefore, products obtained by mixing dispersing agents and acompatibilizer into a resin were studied.

1 wt % of Sample 5 (Rate (3R)=46%) of Example 1 was added as a precursordirectly to LLDPE (polyethylene), and the mixture was kneaded whileapplying shear (a shearing force) thereto with a kneader, two-shaftkneader (extruder) or the like.

It has been publicly known that, when a graphite-based carbon materialsturned into graphene, being highly dispersed in a resin, the tensilestrength increases. Therefore, by measuring a tensile strength of theresin, degrees of exfoliating into graphene and dispersion canrelatively be estimated. The tensile strength was measured with an exacttabletop general-purpose testing machine (AUTOGRAPH AGS-J) manufacturedby Shimadzu Corporation under a condition of test speed of 500 mm/min.

In addition, in order to compare degree of exfoliating into graphene anddispersibility depending on the presence or absence of additives, thefollowing comparisons of three types of (a), (b) and (c) were carriedout.

-   (a) No additives-   (b) a general dispersing agent (zinc stearate)-   (c) a compatibilizer (a graft-modified polymer)

With reference to FIG. 17 showing the measurement results, the resultswill be explained. In addition, in FIG. 17, circles refer to resinmaterials using Sample 1 of the comparative example, and squares referto resin materials using Sample 5 of Example 1,

In case (a) where no additive was added, a difference of the tensilestrengths was small.

In case (b) where the dispersing agent was added, it was revealed thatformation of graphene was promoted to a certain degree in the grapheneprecursor of Sample 5.

In case (c) where the compatibilizer was added, it was revealed thatthat formation of graphene was significantly promoted in the grapheneprecursor of Sample 5. This is because it is considered that, besideseffects to disperse graphene, the compatibilizer binds the graphenelayer-bound bodies and the resin, and acts on them such that thegraphene layer-bound bodies are stripped therefrom, when applying shearin that state.

Zinc stearate is explained above as an example of the dispersing agent.However, those suited for compounds may be selected. As examples of thedispersing agent, anionic (anion) surfactants, cationic (cation)surfactants, zwitterionic surfactants, and nonionic surfactants can bementioned. In particular, anion surfactants and nonionic surfactants arepreferable for graphene. Nonionic surfactants are more preferable. Sincenonionic surfactants are surfactants which do not dissociate into ionsand which show hydrophilic properties by hydrogen bonds with water, asobserved in oxyethylene groups, hydroxyl groups, carbohydrate chainssuch as glucoside, and the like, there is a merit that they can be usedin nonpolar solvents, although they do not have a strength ofhydrophilicity as high as ionic surfactants. Further, this is because,by varying chain lengths of their hydrophilic groups, their propertiescan freely be changed from lipophilic properties to hydrophilicproperties. As anionic surfactants, X acid salts (as for the X acid, forexample, cholic acid, and deoxycholic acid), for example, SDC: sodiumdeoxycholate, and phosphate esters, are preferable. Furthermore, asnonionic surfactants, glycerol fatty acid esters, sorbitan fatty acidesters, fatty alcohol ethoxylates, polyoxyethylene alkyl phenyl ether,alkyl glycosides, and the like are preferable.

EXAMPLE 5

In order to further verify that those obtained when the Rate (3R) is 31%or more are beneficial as graphene precursors, which is described abovein Example 1, an example in which a graphene precursor was kneaded witha resin will be further explained in Example 5. The following explainselastic moduli of resin molded articles in which graphite-based carbonmaterials containing Samples 1 to 7 in Example 1, having Rates (3R)plotted in FIG. 14, were used as precursors.

(1) Using the above-described graphite-based carbon material as aprecursor, 5 wt % of LLDPE (polyethylene: 20201J produced by PrimePolymer Co., Ltd.) and 1 wt % of a dispersant (nonionic surfactant) weremixed in an ion-exchanged water, and the above-described deviceillustrated in FIG. 8 was actuated under the same conditions, wherebygraphene dispersions containing 5 wt % of graphene and graphite-basedcarbon materials were obtained.

(2) 0.6 kg of the graphene dispersion obtained in (1) was immediatelykneaded into a resin of 5.4 kg using a kneader (pressing-type kneaderWDS7-30 produced by Moriyama Co., Ltd.), whereby pellets were produced.The kneading conditions are to be described below. It should be notedthat the mixing ratio between the resin, and the dispersion was selectedso that the amount of the graphene and graphite-based carbon materialsmixed therein was eventually 0.5 wt %.

(3) The pellets produced in (2) were formed into a test piece accordingto JIS K7161 1A (length: 165 mm, width.: 20 mm, thickness: 4 mm) by aninjection molding machine.

(4) The elastic modulus (Mpa) of the test piece produced in (3) wasmeasured under a condition of a test speed of 500 mm/min according toJIS K7161 by a table-top type precision universal tester produced byShimadzu Corporation (AUTOGRAPH AGS-J).

The kneading conditions were as follows.

Kneading temperature: 135° C.

Rotor rotation speed: 30 rpm

Kneading time: 15 minutes

Pressurization in furnace: applying 0.3 MPa for 10 minutes after start,and depressurizing to atmospheric pressure after the 10 minutes elapsed

Here, the dispersion of the above-described graphene dispersion into aresin is considered as follows. As the melting point of a resin isgenerally 100° C. or higher, water evaporates in atmosphere, but in apressing-type kneader, the inside of a furnace can be pressurized. Inthe inside of the furnace, the boiling point of water is raised so thatthe dispersion is kept in a liquid form, whereby an emulsion of thedispersion and the resin can be obtained. After applying pressure for apredetermined time, the inside is gradually depressurized, which causesthe boiling point of water to decrease, thereby allowing water toevaporate. Here, graphene confined in water are left in the resin. Thiscauses graphene and graphite-based carbon materials to be dispersed at ahigh concentration in the resin.

Further, since the graphene and graphite-based carbon materials tend toprecipitate in the graphene dispersion as time elapses, the graphenedispersion is kneaded into the resin preferably immediately after thegraphene dispersion is obtained.

It should be noted that the following may be used as the means forobtaining the emulsion of the dispersion and the resin, other than thepressing kneader: a chemical thruster; a vortex mixer; a homomixer; ahigh-pressure homogenizer; a hydroshear; a flow jet mixer; a wet jetmill; and an ultrasonic generator.

Further, the following may be used as a solvent for the dispersion,other than water: 2-propanol (IPA); acetone; toluene;N-methylpyrrolidone (NMP); and N,N-dimethyl formamide (DMF).

Table 4 illustrates the relationship between the Rates (3R) of around30% and the elastic moduli of resin molded articles. It should be notedthat Sample 00 in Table 4 is a blank Sample in which no precursor waskneaded, Samples 11 and 12 have Rates (3R) between that of Sample 1 andthat of Sample 2, and Sample 21 has a Rate (3R) between that of Sample 2and that of Sample 3.

TABLE 4 Sample No. 00 1 11 12 2 21 3 4 P3/(P3 + P4) — 23% 25% 28% 31%35% 38% 42% Elastic 175 197 196 199 231 249 263 272 modulus (MPa)(Average in 5 times) Difference — 12.4%   12.0%   13.9%   31.7%  42.1%   50.0%   55.6%   from blank Under-10 — 10% 12% 25% 25% 30% 38%62% layers upon dispersion in NMP (Reference)

FIG. 18 and Table 4 prove that the difference of the elastic moduluswith respect to that of Sample 00 (blank) (increase ratio of the elasticmodulus) is approximately uniform around 10% until the Rate (3R) reaches31%; after the Rate (3R) reaches 31%, the difference sharply increasesto 32%; while the Rate (3R) increases from 31% to 42%, the differencemonotonously increases to 50%; and after the Rate (3R) reaches 42%, thedifference slightly increases and converges to around 60%. In this way,when the Rate (3R) is 31% or more, a resin molded article having anexcellent elastic modulus can be obtained. Further, since the amount ofgraphene and graphite-based carbon materials contained in a resin moldedarticle is 0.5 wt %, which is small, influence on properties that theresin originally possesses is small.

It is considered that this tendency attributes to a sharp increase in athin graphite-based carbon material containing graphene having 10 orless layers in contact with a resin after the Rate (3R) reaches 31%.Here, in Example 5, it is impossible to determine the number of layersof graphene by observation with TEM due to influences of a dispersantused for dispersion in water. Then, only for reference, the reason forthe sharp increase described above is considered based on thedistribution of the numbers of layers of the graphite-based carbonmaterial illustrated in Table 4 upon dispersion in NMP. Sample 12 andSample 2 are compared with each other, and it is found that both of theproportions of graphene (the number of layers are 10 or less) were 25%.On the other hand, as illustrated in FIG. 19, as to Sample 2, theproportion of thin ones having less than 15 layers was greater ascompared with Sample 12; in other words, the graphite-based carbonmaterial dispersed as a precursor had a larger surface area, which meansthat the area thereof in contact with the resin sharply increased.

In this way, Example 5 clearly indicates that when the Rate (3R) is 31%or more, a graphite-based carbon material used as a graphene precursortends to be separated into graphene having 10 or less layers and a thingraphite-based carbon material.

EXAMPLE 6

In Example 5 where graphene-like graphite alone was dispersed, anelastic modulus was increased, however a significant increase of atensile strength was not observed.

Thus, experiments were performed by adding the graphene precursorproduced by the above methods and a glass fiber to a resin.

<Various Conditions>

Resin: PP (polypropylene) J707G manufactured by Prime Polymer Co., Ltd.,

Compatibilizer: KAYABRID (006PP manufactured by Kayaku Akzo Corp. Maleicanhydride-modified PP)

Glass fiber (GF): ECS03-631K manufactured by Central Glass Fiber Co.,Ltd. (diameter of 13 μm, length of 3 mm),

Graphite-based carbon material: Graphene precursor (produced by abovemethod),

Mixer: Tumbler mixer (manufactured by SEIWA GIKEN Co., Ltd.),

-   -   <Mixing condition 1: rotation speed 25 rpm×1 min>,

Kneader: Two-shaft extruder (HYPERKTX 30 manufactured by Kobe Steel,Ltd.),

-   -   <Kneading condition 1: cylinder temperature of 180° C., rotor        rotation speed of 100 rpm, discharge rate of 8 kg/h>

Test piece: JIS K7139 (170 mm×20 mm×t4 mm)

Measuring device: Exact tabletop general-purpose testing machineAUTOGRAPH AGS-J manufactured by Shima.dzu Corp.

<Experimental Procedures>

-   Step 1. 40 wt % of a glass fiber (OF), 4 wt % of a compatibilizer,    and 56 wt % of a resin are pre-mixed in a tumbler mixer under the    mixing condition 1, and then kneaded with a two-shaft extruder under    the kneading condition 1 to obtain a master batch 1.-   Step 2. 12 wt % of a graphene precursor having a different Rate (3R)    as shown in Table 5 and 88 wt % of a resin are pre-mixed with a    tumbler mixer under the mixing condition 1, and then kneaded with a    two-shaft extruder under the kneading condition 1 to obtain a master    batch 2.-   Step 3. 25 wt % of the mater batch 1, 25 wt % of the mater batch 2,    and 50 wt % of a resin are pre-mixed with a tumbler mixer under the    mixing condition 1, and then kneaded with a two-shaft extruder under    the kneading condition 1.-   Step 4. A kneaded mixture obtained in Step 3 was formed into a test    piece with an injection molding machine and changes in mechanical    strength thereof were observed at a test speed of 500 mm/min    according to JIS K7139.

In order to confirm an effect of graphene-like graphite, experimentswere performed with a Rate (3R) of 23% (Sample 1), 31% (Sample 2), 35%(Sample 21), and 42% (Sample 4) with a mixture ratio shown in Table 5.

TABLE 5 Mixture ratio (wt %) Graphene precursor Rate (3R) = Rate (3R) =Rate (3R) = Rate (3R) = Tensile Bending 23% 31% 35% 42% strength modulusPP Compatibilizer GF (Sample 1) (Sample 2) (Sample 21) (Sample 4) (MPa)(GPa) Example 6-1 86 1 10 3 — — — 73 3.9 Example 6-2 86 1 10 — 3 — — 995.6 Example 6-3 86 1 10 — — 3 — 108 1 6.2 Example 6-4 86 1 10 — — 3 1166.5 Comparative 100 — — — — — — 25 1.2 example 6-1 Comparative 89 1 10 —— — — 70 3.8 example 6-2 Comparative 96 1 — — 3 — — 27 2.5 example 6-3

From Table 5 and FIG. 20, it was observed that a tensile strength inExamples 6-2, 6-3, and 6-4 was higher than in Example 6-1 andComparative examples 6-1, 6-2 and 6-3. In particular, when the Rate (3R)of the graphene precursor reached 31% or more, a remarkable tendency wasobserved in a tensile strength, which increased by 30% or more ascompared with cases of the Rate (3R) being 0% (Comparative example 6-2)(strictly speaking, this is not the same as Rate (3R) 0%. Since agraphene precursor was not added, the 0% data shouldn't be plotted tothe same graph. Nevertheless the data is plotted at the position of 0%for convenience. Hereinafter, 0% has the same meaning.) and the Rate(3R) being 23% (Example 6-1). It is noted that data from Comparativeexamples 6-1 and 6-3, in which CF is not included, are not plotted inFIG. 20.

Further, similarly in the case of a tensile strength, it was observedthat a bending modulus in Examples 6-2, 6-3, and 6-4 was higher than inExample 6-1 and Comparative examples 6-1, 6-2 and 6-3. In particular,when the Rate (3R) of the graphene precursor reached 31% or more, aremarkable tendency was observed in a bending modulus, which increasedby 40% or more as compared with cases of the Rate (3R) being 0%(Comparative example 6-2) and the Rate (3R) being 23% (Example 6-1)

When the graphene precursors having the Rate (3R) of 31% or more(Examples 6-2, 6-3, and 6-4) are used together with GF, a tensilestrength and a bending modulus become higher. This is because, it isspeculated that, graphene-like graphite having a thickness of 0.3 toseveral tens of nm and a size of several nm to 1 μm was dispersed in PP,thereby increasing an elastic modulus of PP itself, and in the sametime, the graphene-like graphite brought into contact with GE, which wastightly bound to PP by virtue of a compatibilizer thus hardly coming offPP, executed a so-called wedge action on GE. As a result, a tensilestrength and a bending modulus were both increased by a synergisticeffect of increasing an elastic modulus of PP itself and executing awedge action. This situation can be expressed by the following parable:after driving a barbed stake into a ground, it can easily come off amuddy ground, but can hardly come off a well-trodden ground. As anotherfactor causing this, it is speculated that addition of thecompatibilizer promotes exfoliation of the graphene-like graphite, etc.from the graphite-based carbon material, thereby causing flakedgraphene-like graphite to be present in a larger amount.

When the Rate (3R) is less than 31% (Example 6-1) it is considered thatan amount of graphene-like graphite that is dispersed is too small sothat an effect of adding a graphene precursor is not sufficientlyexerted.

When the Rate (3R) is 35% or more (Examples 6-3 and 6-4), a bendingmodulus and a tensile strength are excellent as compared with cases ofthe Rate (3R) being equal to or lower than that. The reason isconsidered that the amount of graphene-like graphite causing an increaseof an elastic modulus of PP becomes larger as compared with the case ofthe Rate (3R) being 31% (Example 6-2).

For reference, an explanation is given on photographed images ofgraphene precursors taken by a scanning electron microscope (SEM). Thegraphene precursors obtained in Example 1 are a laminate of flakygraphite having a length of 7 μm and a thickness of 0.1 μm as shown forexample in FIGS. 21 and 22.

Further, graphene-like graphite dispersed in a resin can be observed bya scanning electron microscope (SEM) and the like after being formedinto a test piece and cut by a precision high-speed saw (TechCut5manufactured by Allied High Tech Products, Inc.) and the like. Forexample, FIG. 23 shows a cross section of a resin in which a carbonnanotube and graphene-like graphite are dispersed, where the carbonnanotube is represented by a linear part and the graphene-like graphiteis represented by a white spot part. The graphene-like graphite is alaminate of flaky graphite having a thickness of 3.97 nm as shown forexample in FIG. 24.

EXAMPLE 7

Experiments were performed to obtain a resin molded article using thegraphene precursor produced in the above methods.

<Various Conditions>

Resin: PA66 (66 nylon) 13008 manufactured by Asahi Kasei Corp.,

Compatibilizer: KAYABRII) (006PP manufactured by Kayaku Akzo Corp.Maleic anhydride-modified PP)

Glass fiber (GF): ECS03-631K (diameter of 13 pin, length of 3 mm)manufactured by Central Glass Fiber Co., Ltd.),

Graphite-based carbon material: Graphene precursor (obtained by theabove methods),

Mixer: Tumbler mixer (manufactured by SEIWA GIKEN Co., Ltd.),

-   -   <Mixing condition 1: rotation speed 25 rpm×1 min>,

Kneader: Two-shaft extruder (HYPERKTX 30 manufactured by Kobe Steel,Ltd.),

-   -   <Kneading condition 2: cylinder temperature of 280° C., rotor        rotation speed of 200 rpm, discharge rate of 12 kg/h>

Test piece: JIS K7139 (170 mm×20 mm×t4 m>,

Measuring device: Exact tabletop general-purpose testing machineAUTOGRAPH AGS-J manufactured by Shimadzu Corp.

<Experimental Procedures>

-   Step 1. 40 wt % of a glass fiber (GF), 4 wt % of a compa.tibilizer,    and 56 wt % of a resin are pre-mixed in a tumbler mixer under the    mixing condition 1, and then kneaded with a two-shaft extruder under    the kneading condition 2 to obtain a master batch 1.-   Step 2. 12 wt % of a graphene precursor having a different Rate (3R)    as shown in Table 6 and 88 wt % of a resin are pre-mixed in a    tumbler mixer under the mixing condition 1, and then kneaded with a    two-shaft extruder under the kneading condition 2 to obtain a master    batch 2.-   Step 3. 37.5 wt % of the mater batch 1, 25 wt % of the mater batch    2, and 37.5 wt % of a resin are pre-mixed in a tumbler mixer under    the mixing condition 1, and then kneaded with a two-shaft extruder    under the kneading condition 2.-   Step 4. A kneaded mixture obtained in Step 3 was formed into a test    piece with an injection molding machine and changes in mechanical    strength thereof were observed at a test speed of 500 mm/min    according to JIS K7139.

In order to confirm an effect of graphene-like graphite, experimentswere performed with a Rate (3R) of 23% (Sample 1), 31% (Sample 2), 35%(Sample 21), and 42% (Sample 4) with a mixture ratio shown in Table 6.

TABLE 6 Mixture ratio (wt %) Graphene precursor Rate (3R) = Rate (3R) =Rate (3R) = Rate (3R) = Tensile Bending 23% 31% 35% 42% strength modulusPA66 Compatibilizer GF (Sample 1) (Sample 2) (Sample 21) (Sample 4)(MPa) (GPa) Example 7-1 80.5 1.5 15 3 — — — 111 4.9 Example 7-2 80.5 1.515 — 3 — — 138 6.2 Example 7-3 80.5 1.5 15 — — 3 — 143 6.6 Example 7-480.5 1.5 15 — — — 3 146 6.8 Comparative 100 — — — — — — 57 2.7 example7-1 Comparative 83.5 1.5 15 — — — — 107 4.8 example 7-2 Comparative 95.51.5 — — 3 — — 90 3.3 example 7-3

From Table 6 and FIG. 25, it was observed that a tensile strength inExamples 7-2, 7-3, and 7-4 was higher than in Example 7-1 andComparative examples 7-1, 7-2, and 7-3. In particular, when the Rate(3R) of the graphene precursor reached 31% or more, a remarkabletendency was observed in a tensile strength, which increased by 20% ormore as compared with cases of the Rate (3R) being 0% (Comparativeexample 7-2) and the Rate (3R) being 23% (Example 7-1). It is noted thatdata from Comparative examples 7-1 and 7-3, in which GE is not included,are not plotted in FIG. 25.

Further, similarly in the case of a tensile strength, it was observedthat a bending modulus in Examples 7-2, 7-3, and 7-4 was higher than inExample 7-1 and Comparative examples 7-1, 7-2 and 7-3. In particular,when the Rate (3R) of the graphene precursor reached 31% or more, aremarkable tendency was observed in a bending modulus, which increasedby 20% or more as compared with cases of the Rate (3R) being 0%(Comparative example 7-2) and the Rate (3R) being 23% (Example 7-1).

It is considered that a tensile strength and a bending modulus areimproved by the same reason as explained in Example 6.

From Examples 6 and 7, it was observed that a tensile strength and abending modulus were improved regardless of a resin serving as a basematerial. An explanation is given on a case where a graphene precursoris added together with CF. When the graphene precursors had the Rate(3R) of 23% (Examples 6-1 and 7-1), it was observed that a tensilestrength and a bending modulus were slightly improved regardless of aresin serving as a base material as compared with cases where a grapheneprecursor was not added (Comparative examples 6-2 and 7-2), while whenthe graphene precursors in use had the Rate (3R) of 31% or more, it wasobserved that a tensile strength and a bending modulus were sharplyimproved (by 10% or more).

EXAMPLE 8

Experiments were performed by adding the graphene precursor produced inthe above methods and a reinforcing material to a resin.

In Example 8, a glass fiber (GF), a carbon fiber (CF), talc, and silicawere used as a reinforcing material to confirm an effect caused by ashape of a reinforcing material. Except for a reinforcing material,experimental conditions and the like are the same as in Example 6.

As shown in FIG. 27, GF and CF, functioning as a reinforcing material,have a diameter of several tens of μm and a length of several hundredsof μm in a string-like or linear shape. Talc has a representative lengthof several to several tens of μm and a thickness of several hundreds ofrim in a flake-like shape, while silica has a diameter of several tensof nm to several μm in a particulate shape.

TABLE 7 Mixture ratio (wt %) Grapheme precursor Rate (3R) = TensileBending 31% strength modulus PP Compatibilizer GF CF Talc Silica (Sample2) (MPa) (GPa) Example 6-2 86 1 10 — — — 3 99 5.6 Example 8-1 86 1 — 10— — 3 168 6.7 Example 8-2 86 1 — — 10 — 3 45 4.0 Example 8-3 86 1 — — —10 3 33 3.8 Comparative 89 1 10 — — — — 70 3.8 example 6-2 Comparative89 1 — 10 — — — 130 5.2 example 8-1 Comparative 89 1 — — 10 — — 35 3.5example 8-2 Comparative 89 1 — — — 10 — 32 1.9 example 8-3 Comparative100 — — — — — 25 1.2 example 6-1

As shown in Table 7 and FIG. 26, a tensile strength and a bendingmodulus are improved in all cases where a reinforcing material is addedas compared with Comparative example 6-1 where a reinforcing material isnot added. A comparison was made between cases where a reinforcingmaterial and a graphene precursor were added (Examples 6-2, 8-1, 8-2,and 8-3) and cases where a reinforcing material alone was added(Comparative examples 6-2, 8-1, 8-2, and 8-3). When GE was added as areinforcing material together with a graphene precursor, a tensilestrength and a bending modulus were both improved by 1.4 times and 1.4times, respectively (a rate change observed in Example 6-2 overComparative example 6-2). Similarly, a tensile strength and a bendingmodulus were improved by 1.3 times and 1.3 times, respectively in a caseof CE, 1.3 times and 1.1 times, respectively in a case of talc, and 1.0times and 2.0 times, respectively in a case of silica. From these, itwas found that using a reinforcing material in a string-like, linear, orflake-like shape together with a graphene precursor improved a tensilestrength and a bending modulus by 10% or more, thus being preferable. Itis speculated that a nano-reinforcing material in a string-like, linearor flake-like shape, by having a wide surface area per unit mass due toits shape, is highly effective in improving a tensile strength as wellas capable of increasing a bending modulus, therefore having highcompatibility with graphene-like graphite. It was also revealed that, asa reinforcing material in a string-like, linear, or flake-like shape,the one having an aspect ratio of 5 or more is particularly preferable.In contrast, a reinforcing material having an aspect ratio of 5 or less,such as silica, resulted in increasing a bending modulus only. It isnoted that an aspect ratio of a material having a flake-like shape canbe obtained by calculating a ratio of an average thickness to a lengthof the longest part. An aspect ratio mentioned here can be calculated byusing an average value of a diameter or a thickness and an average valueof a length, described in a catalog and the like of a reinforcingmaterial. Especially, when a catalog and the like are not available, amaterial is observed by an electron microscope such as SEM in anarbitrary number to obtain average values of length and thicknessthereof, from which an aspect ratio is calculated.

EXAMPLE 9

Next, experiments were performed to obtain a resin molded article usingthe graphene precursor produced in the above methods.

The experiments were performed with a mixture ratio of the grapheneprecursor having the Rate (3R) of 31% to a reinforcing material underconditions shown in Table 8. Experimental conditions and the like arethe same as in Example 6.

TABLE 8 Mixture ratio (wt %) Graphene precursor Rate (3R) = Bending 31%Tensile mod- (Sam- strength ulus PP Compatibilizer GF ple 2) (MPa) (GPa)Example 9-1 88 1 10 1 87 4.7 Example 6-2 86 1 10 3 99 5.6 Example 9-2 841 10 5 107 6.3 Example 9-3 81 1 10 8 116 6.9 Example 9-4 79 1 10 10 1207.1 Example 9-5 74 1 10 15 121 7.2 Example 9-6 88.5 1 10 0.5 80 4.5Example 9-7 88.7 1 10 0.3 79 4.2 Example 9-8 88.9 1 10 0.1 73 4.0Comparative 100 — — — 25 1.2 example 6-1 Comparative 89 1 10 — 70 3.8example 6-2

As shown in Table 8 and FIG. 28, when the mixture ratio of the grapheneprecursor to the reinforcing material became more than 1 (Example 9-4),it was observed that a tensile strength and a bending modulus stayed atmostly the same values and their characteristics became saturated.Further, when the mixture ratio of the graphene precursor is 10 or more,an impact on properties of a base material becomes significant. On theother hand, when the mixture ratio was 1/100 (Example 9-8), it wasobserved that a tensile strength and a bending modulus were increased by4% or more and 10% or more, respectively, as compared with Comparativeexample 6-2 where a graphene precursor was not added. Further, it wasobserved that a tensile strength was sharply increased when the mixtureratio was 1/10 (Example 6-2) or more, while a bending modulus wassharply increased when the mixture ratio was 1/3 (Example 9-1) or more.

Based on these, a lower limit of the mixture ratio is 1/100 or more,preferably 1/10 or more, and an upper limit thereof is 10 or less,preferably 1 or less.

It is noted that data from Comparative example 6-1 where GF is notincluded is not plotted in FIG. 28.

In Example 6-9, the graphene precursor is produced by a radiowaveforce-based treatment and/or a physical force-based treatment asdescribed above, thus it is not necessary to perform anoxidation/reduction treatment. Further since a reduction treatment isnot necessary to produce a test piece, high temperature is not required,as a result, producing a test piece is readily performed.

The foregoing explained the embodiments of the present invention usingdrawings, however it should be understood that the specificconstitutions are not at all restricted to these embodiments, andchanges and additions are also included in the present invention withoutdeparting from the gist of the present invention.

Examples of a base material for dispersing a reinforcing material and agraphite-based carbon material include the following. It is noted that amixture ratio of a base material may be smaller than that of areinforcing material or a graphite-based carbon material. Further, abase material may be annihilated by combustion, oxidation, vaporization,evaporation, and the like when in use. For example, when a base materialas a coating agent and the like is a volatile solvent, the base materialis carbonized by combustion, as is the case for a C/C composite.

Examples of a resin include thermoplastic resins such as polyethylene(PE), polypropylene (PP), polystylene (PS), polyvinyl chloride (PVC),ABS resins (ABS), polylactic acid (PLA), acrylic resins (PMMA),polyamide/nylon (PA), polyacetal (POM), polycarbonate (PC), polyethylenetelephthalate (PET), cyclic polyolefin (COP), polyphenylene sulfide(PPS), polytetrafluoroethylene (PTFE), polysulfone (PSF), polyamideimide (PAI), thermoplastic polyimide (PI), polyether ether ketone(PEEK), crystalline polymers (LCP), and the like. In addition, amongsynthetic resins: as thermosetting resins or ultraviolet curing resins,included are epoxy resins (EP), phenolic resins (PF), melamine resins(MF), polyurethanes (PUR), and unsaturated polyester resins (UP) and thelike; as conductive polymers, included are PEDOT, polythiophene,polyacetylene, polyaniline, polypyrrole, and the like; as fibers,included are fibrous nylon, polyesters, acryl, vinylon, polyolefin,polyurethane, rayon and the like; as elastomers, included are isoprenerubbers (IR), butadiene rubbers (BR), styrene/butadiene rubbers (SBR),chloroprene rubbers (CR), nitrile rubbers (NBR), polyisobutylenerubbers/butyl rubbers (IIR), ethylene propylene rubbers (EPM/EPDM),chlorosulfonated polyethylene (CSM), acrylic rubbers (ACM),epichlorohydrin rubbers (CO/ECO), and the like; as thermosettingresin-based elastomers, included are some urethane rubbers (U), siliconerubbers (Q), fluorine-containing rubbers (FKM), and the like; and, asthermoplastic elastomers, included are elastomers based on styrene,olefin, polyvinyl chloride, urethane, and amide.

Examples of an inorganic material include concrete, ceramics, gypsum,metal powders, and the like.

Examples of a reinforcing material include the following.

As a metal material included are silver nanoparticles, coppernanoparticles, silver nanowires, copper nanowires, flaky silver, flakycopper, iron powders, zinc oxide, fibrous metal (boron, tungsten,alumina, and silicon carbide), and the like.

As a carbon material included are carbon black, carbon fibers, CNT,graphite, activated carbon, and the like.

As a nonmetal material except for carbon, included are glass fibers,nanocelluloses, nanoclay (clay mineral such as montmorillonite), aramidfibers, polyethylene fibers, and the like.

In addition, as an example of natural graphite for producing agraphite-based carbon material useful as a graphene precursor, particlesof 5 mm or less of a natural graphite material (flaky graphite ACE-50manufactured by Nippon Graphite Industries, ltd.) is described above.However, as for the natural graphite, products which are flaky graphite,being pulverized into 5 mm or less, and which have a Rate (3R) of lessthan 25% and an intensity ratio P1/P2 of less than 0.01 are preferable,from a viewpoint that they are easily-available corresponding to recenttechnology development, natural graphite-like graphite (in whichcrystals are stacked in layers) can be artificially synthesized, thusraw materials for graphene and graphene-like graphite are not limited tonatural graphite (mineral). Artificial graphite having a high degree ofpurity is preferably used for a purpose of controlling a metal content.Further, as long as a Rate (3R) is 31% or more, artificial graphite,which is not produced by a physical force-based treatment or a radiowaveforce-based treatment described above, may be used.

It should be noted that a graphite-based carbon material useful as agraphene precursor is generally referred to as graphene, a grapheneprecursor, a graphene nanoplatelet (GNP), few-layer graphene (FLG),nanographene, and the like, however it is not particularly limitedthereto.

INDUSTRIAL APPLICABILITY

The present invention covers a composite reinforcing material havingstrength, and an application field thereof is not limited. For example,the following fields are included in the present invention.

(1) Examples in which a base material is an organic material (resins andplastics)

(1-1) Conveyance for transporting

Airplanes, automobiles (passenger cars, trucks, buses, etc.), ships,cases for toys, etc., structure members such as parts. (for structuremembers, composite resins, modified resins, fiber reinforced resins, andthe like)

(1-2) General-purpose articles

Furniture, home electric appliance, household supplies, cases for toys,etc., structure members such as parts.

(1-3) 3D printers

Various kinds of molding materials, such as resin filaments and DVcuring resins, used in fused deposition modeling (FDM),stereolithography (SLA), powder sticking lamination, selective lasersintering (SLS), and multi jet modeling (MJM, ink jet modeling)

(1-4) Coating agents

A composite reinforcing material is, together with a resin, dispersed inan organic solvent and used to coat a surface of subjects by spraying orpainting, etc. Such a coating agent improves strength of subjects andalso has effects of water repellency, rust resistance, ultraviolet rayresistance, etc. Examples of application include use for external andinternal coating of constructions (bridge piers, buildings, walls,roads, etc.), automobiles, airplanes, etc., and for resin moldedarticles such as helmets and protectors.

(2) Examples in which a base material is an inorganic material

Fiber-reinforced structure members, such as cement (concrete, mortar),gypsum boards, ceramics, and C/C composites (carbon fiber-reinforcedcarbon composite materials) Products made by dispersing graphene-likegraphite and a reinforcing material in these inorganic materials as abase material.

(3) Metal materials as a base material

Structure members, such as aluminum, stainless steel, titanium, brass,bronze, soft steel, nickel alloy, and tungsten carbide. (for structuremembers, fiber-reinforced metal and the like). Products made bydispersing graphene-like graphite and a reinforcing material in thesemetal materials as a base material.

The invention claimed is:
 1. A method of producing a compositereinforcing material, comprising a step of kneading at least agraphite-based carbon material and a reinforcing material into a polymerbase material, the graphite-based carbon material having a rhombohedralgraphite layer (3R) and a hexagonal graphite layer (2H), wherein a Rate(3R) of the rhombohedral graphite layer (3R) and the hexagonal graphitelayer (2H), based on an X-ray diffraction method, which is defined byfollowing Equation 1 is 31% or more:Rate (3R)=P3/(P3+P4)×100  Equation 1 wherein P3 is a peak intensity of a(101) plane of the rhombohedral graphite layer (3R) based on the X-raydiffraction method, and P4 is a peak intensity of a (101) plane of thehexagonal graphite layer (2H) based on the X-ray diffraction method. 2.The method of producing the composite reinforcing material according toclaim 1, wherein the reinforcing material is a microparticle having astring-like, linear, or flake-like shape.
 3. The method of producing thecomposite reinforcing material according to claim 2, wherein themicroparticle has an aspect ratio of 5 or more.
 4. The method ofproducing the composite reinforcing material according to claim 1,wherein a weight ratio of the graphite-based carbon material to thereinforcing material is 1/100 or more and less than
 10. 5. The method ofproducing the composite reinforcing material according to claim 2,wherein a weight ratio of the graphite-based carbon material to thereinforcing material is 1/100 or more and less than
 10. 6. The method ofproducing the composite reinforcing material according to claim 1,wherein a compatibilizer is added.
 7. A method of producing a compositereinforcing material, comprising a step of kneading at least agraphite-based carbon material and a reinforcing material into a polymerbase material, so that graphene is partially exfoliated from thegraphite-based carbon material and dispersed in the base material, thegraphene being a crystal of a mean size of 100 nm or more and formed ina flake-like or sheet-like shape having 10 or less layers, a proportionof the graphene having 10 layers or less being 25% or more after thekneading step, the graphite-based carbon material having a rhombohedralgraphite layer (3R) and a hexagonal graphite layer (2H), wherein a Rate(3R) of the rhombohedral graphite layer (3R) and the hexagonal graphitelayer (2H), based on an X-ray diffraction method, which is defined byfollowing Equation 1 is 31% or more:Rate (3R)=P3/(P3+P4)×100  Equation 1 wherein P3 is a peak intensity of a(101) plane of the rhombohedral graphite layer (3R) based on the X-raydiffraction method, and P4 is a peak intensity of a (101) plane of thehexagonal graphite layer (2H) based on the X-ray diffraction method. 8.The method of producing the composite reinforcing material according toclaim 7, wherein the reinforcing material is a microparticle having astring-like, linear, or flake-like shape.
 9. The method of producing thecomposite reinforcing material according to claim 8, wherein themicroparticle has an aspect ratio of 5 or more.
 10. The method ofproducing the composite reinforcing material according to claim 7,wherein a weight ratio of the graphite-based carbon material to thereinforcing material is 1/100 or more and less than
 10. 11. The methodof producing the composite reinforcing material according to claim 8,wherein a weight ratio of the graphite-based carbon material to thereinforcing material is 1/100 or more and less than
 10. 12. The methodof producing the composite reinforcing material according to claim 7,wherein a compatibilizer is added.